hashutil.github_signature does not recognize sha argument

Description of Issue

Executing salt <minion> hashutil.github_signature '{"ref":....} ' 'shared secret' 'sha1=<key> returns the error:

ERROR executing 'hashutil.github_signature': The following keyword arguments are not valid: sha1=c12560e6fe48bf2a1e96119a81ffb9d3ee033717

Setup

GitHub Webhook configured for push event.

For the string, cut-n-paste either the payload from GitHub Webhook Recent Deliveries request section or via the event bus. challenge_hmac comes from either location.

Steps to Reproduce Issue

(Include debug logs if possible and relevant.)

Versions Report

(Provided by running salt --versions-report. Please also mention any differences in master/minion versions.)

salt --versions-report
Salt Version:
           Salt: 3001

Dependency Versions:
           cffi: Not Installed
       cherrypy: unknown
       dateutil: 2.6.1
      docker-py: Not Installed
          gitdb: 2.0.3
      gitpython: 2.1.8
         Jinja2: 2.10
        libgit2: Not Installed
       M2Crypto: Not Installed
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.5.6
   mysql-python: 1.3.10
      pycparser: Not Installed
       pycrypto: 2.6.1
   pycryptodome: 3.4.7
         pygit2: Not Installed
         Python: 3.6.9 (default, Apr 18 2020, 01:56:04)
   python-gnupg: 0.4.1
         PyYAML: 3.12
          PyZMQ: 17.1.2
          smmap: 2.0.3
        timelib: Not Installed
        Tornado: 4.5.3
            ZMQ: 4.2.5

System Versions:
           dist: ubuntu 18.04 Bionic Beaver
         locale: UTF-8
        machine: x86_64
        release: 4.15.0-111-generic
         system: Linux
        version: Ubuntu 18.04 Bionic Beaver

Start with the hashutil.github_signature entry point and reproduce the Salt 3001 command using the GitHub push-event payload and shared secret described in the issue. Trace how the sha1= argument is handled; done means the argument is recognized instead of reported as an invalid keyword argument and the signature check works for the supplied payload.